Light source device and display device

ABSTRACT

A light source device includes a discharge tube, a reflector for reflecting a light radiated from the discharge tube, and support members for supporting the discharge tube to the reflector. The support member or the discharge tube is formed of a heat insulating structure so as to prevent a temperature drop of a portion of the discharge tube near electrodes thereof. By this arrangement, it is possible to prolong the operational life of the discharge tube.

This application is divisional of application Ser. No. 11/315,232, filedDec. 23, 2005, which is a continuation of application Ser. No.10/663,708, filed on Sep. 17, 2003, now U.S. Pat. No. 7,070,291, whichis a continuation of PCT/JP 02/02622 filed Mar. 19, 2002, which claimsthe priority of Japanese Application No. 2001-078546 filed Mar. 19,2001, which is incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a light source device having adischarge tube emitting light by a discharge in a lean gas.

BACKGROUND ART

A backlight, as a light source device of a display device such as aliquid crystal display device, uses a light source device comprising oneor a plurality of discharge tubes and a reflector. The discharge tube isa cold cathode tube, in which mercury is contained in a lean gas (suchas Ar and Ne) and a fluorescent material is coated on the tube wall.Electrodes are provided in both ends of the discharge tube. Thedischarge tube is supported by the reflector with support members whichare arranged at positions near the electrodes of the discharge tube. Thebacklight also has a light guide plate, and the light source device isarranged on the side of the light guide plate.

When the high voltage is applied to the electrodes of the dischargetube, electrons are emitted by the electrodes and impinge against themercury gas in the discharge tube. The mercury gas produces ultravioletlight, which impinges against the fluorescent material in the dischargetube to emit visible light. As the amount of the mercury gas in thedischarge tube is reduced, the amount of emitted light is reduced and anoperational life thereof ends. Usually, a sufficient amount of mercurygas is sealed in the discharge tube to enable the discharge tube to havea long life, but there are discharge tubes having extremely shortoperational lives.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a light source devicecapable of a long operational life of a discharge tube.

A light source device, according to the first aspect of the presentinvention, comprises a discharge tube, a reflector for reflecting alight radiated from the discharge tube, and support members forsupporting the discharge tube to the reflector, said support membersbeing formed of a heat insulating structure so as to prevent atemperature drop of a portion of the discharge tube near electrodes ofthe discharge tube.

A light source device, according to the second aspect of the presentinvention, comprises a discharge tube, a reflector for reflecting alight radiated from the discharge tube, and support members forsupporting the discharge tube to the reflector, the discharge tube beingformed of a partially heat insulating structure so as to prevent atemperature drop of a portion of the discharge tube near electrodes ofthe discharge tube.

A light source device, according to the third aspect of the presentinvention, comprises a discharge tube, a reflector for reflecting alight radiated from the discharge tube, and support members forsupporting the discharge tube to the reflector, the support membersbeing arranged at positions inward from ends of electrodes of thedischarge tube so as to prevent a temperature drop of a portion of thedischarge tube near electrodes of the discharge tube.

A light source device, according to the fourth aspect of the presentinvention, comprises a discharge tube, a reflector for reflecting alight radiated from the discharge tube, support members for supportingthe discharge tube to the reflector, and a heat conduction membercontacting a central portion of the discharge tube.

In these arrangements, generally, the operating life of the dischargetube will end if the mercury contained in the discharge tube isconsumed. Consumption of mercury occurs in such a manner that gaseousmercury in the discharge tube reacts with particles of metal of theelectrodes (for example, Ni) caused by sputtering with electrons and isadhered to and captured by the inner surface of the discharge tube. Asufficiently large amount of mercury is usually inserted in thedischarge tube, it takes much time for mercury to be consumed and,therefore, the operating life of the discharge tube is guaranteed tosome extent.

However, there are several discharge tubes among many discharge tubeswhich have extremely short operating life. According to the inventor'sstudy, the extremely short operating life is caused by the followingreason. That is, a portion of the discharge tube near the electrodes isprimarily a portion at which the largest amount of heat is generated andthe temperature is higher, but in the structure in which the dischargetube is supported to the reflector by the support members, heat of thedischarge tube is thermally conducted to the reflector through thesupport members and further from the reflector to the housing of thedisplay device, so that the temperature of the portion of the dischargetube near the electrodes becomes the lowest within the discharge tube.Also, the support members are arranged at positions near the electrodesof the discharge tube, the reflector is generally made of metal, and thesupport members are made of silicone so as to withstand the high voltageapplied to the electrodes. Therefore, heat of the discharge tube isliable to be conducted to the reflector through the support members.

Mercury exists in the discharge tube in a gaseous state as well as in anon-gaseous state (liquid or solid). The liquid mercury is collected atthe lowest temperature point in the discharge tube (because aconcentration gradient is produced because of a difference in asaturated vapor pressure due to a temperature difference, mercury isconveyed by diffusion). Particles of metal of the electrodes caused bysputtering with electrons are deposited on the thus collected liquidmercury, and produces a thin membrane on the liquid mercury. Thismembrane prevents the mercury from evaporating, and the amount of thegaseous mercury in the discharge tube is reduced. If the amount of thegaseous mercury is reduced, the discharge tube becomes dark and theoperating life thereof is short.

Accordingly, in the present invention, a shortened operational life ofthe discharge tube is prevented by adopting the above-describedarrangements so that the portion of the discharge tube near theelectrodes of the discharge tube does not become the lowest temperaturepoint and so that the liquid mercury is not captured and enclosed by theparticles of metal of the sputtered electrodes, whereby the amount ofthe gaseous mercury is not reduced.

The above-described light source device can be used as a light sourcedevice of an information processing apparatus and a display device.

Further, the present invention provides an information processingapparatus comprising a light source device and a light valve receiving alight emitted by the light source device, the light source deviceincluding a discharge tube, a reflector for reflecting a light radiatedfrom the discharge tube, support members for supporting the dischargetube to the reflector, and a layer of heat insulating material arrangedbetween the discharge tube and the support member or between the supportmember and the reflector.

Further, the present invention provides a display device comprising alight source device and a light valve receiving a light illuminated bythe light source device, the light source device including a dischargetube, a reflector for reflecting a light radiated from the dischargetube, support members for supporting the discharge tube to thereflector, and a layer of heat insulating material arranged between thedischarge tube and the support member or between the support member andthe reflector.

Further, the present invention provides a light source device comprisinga discharge tube, a reflector for reflecting a light radiated from thedischarge tube, and support members for supporting the discharge tube tothe reflector, the reflector being made of a resin.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a view showing the notebook type personal computer includingthe light source device according to the present invention;

FIG. 2 is a view showing the display device including the light sourcedevice of the present invention;

FIG. 3 is a plan view of the light guide plate and the light sourcedevice of the display device of FIG. 1;

FIG. 4 is a sectional view of the light guide plate and the light sourcedevice of FIG. 3;

FIG. 5 is a sectional view showing the discharge tube;

FIG. 6 is a sectional view of the light source device including thedischarge tube and the reflector;

FIG. 7 is a sectional view of the light source device, taken along theline VII-VII in FIG. 6;

FIG. 8 is a sectional view of the light source device including thedischarge tube and the reflector according to another example;

FIG. 9 is a sectional view of the support member of FIG. 8;

FIG. 10 is a sectional view of the light source device including thedischarge tube and the reflector according to a further example;

FIG. 11 is a sectional view of the light source device including thedischarge tube and the reflector according to a further example;

FIG. 12 is a sectional view of the light source device including thedischarge tube and the reflector according to a further example;

FIG. 13 is a sectional view of the light source device including thedischarge tube and the reflector according to a further example;

FIG. 14 is a sectional view of the light source device including thedischarge tube and the reflector according to a further example; and

FIG. 15 is a sectional view of the light source device including thedischarge tube and the reflector according to a further example.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will be explained hereinafter withreference to the accompanying drawings. FIG. 1 is a view showing thenotebook type personal computer including the light source deviceaccording to the embodiment of the present invention, and FIG. 2 is aview showing the display device including the light source deviceaccording to the present invention.

In FIG. 1, the notebook type personal computer 1 comprises a body 3having a keyboard 2 and electronic circuits, and a display part 5 havinga display 4 such as a liquid crystal display device. The display part 5has a light source device 18. The notebook type personal computer 1 ofFIG. 1 includes one light source device 18, but it is possible toarrange two light source devices 18, as in the case of the displaydevice 6 of FIG. 2.

In FIG. 2, the display device 6 comprises a body 8 having a display 7such as a liquid crystal display device and electronic circuits. Thebody 8 has light source devices 18. The display device 6 of FIG. 2includes two light source devices 18, but it is possible to arrange onelight source device 18, as in the case of the notebook type personalcomputer 1 of FIG. 1.

FIG. 3 is a plan view of the light guide plate and the light sourcedevice of the display 4 of FIG. 1, and FIG. 4 is a sectional view of thelight guide plate and the light source device of FIG. 3. In FIGS. 3 and4, the display 4 includes a liquid crystal display panel 12 and abacklight 14. The backlight 14 includes a light guide plate 16, thelight source devices 18 arranged at the side of the light guide plate16, a scattering reflection plate 20 arranged below the light guideplate 16, and a scattering plate 22 arranged above the light guide plate16.

The light source device 18 comprises a discharge tube 24 and a reflector26. A part of the light emitted by the discharge tube 24 is madedirectly incident to the light guide plate 16, and another part of thelight outgoing from the discharge tube 24 is reflected by the reflector26 to be made incident to the light guide plate 16. The light travelswithin the light guide plate 16, is reflected by the scatteringreflection plate 20 to leave the light guide plate 16 toward the liquidcrystal display panel 12, and is made incident to the liquid crystaldisplay panel 12 after being scattered by the scattering plate 22. Theliquid crystal display panel 12 forms an image, and the light suppliedfrom the light source device 14 illuminates the image formed by theliquid crystal display panel 12, so that a viewer can see a brightimage.

FIG. 5 is a sectional view showing the discharge tube 24, and FIG. 6 isa sectional view showing the light source device 18 including thedischarge tube 24 and the reflector 26. FIG. 7 is a sectional view ofthe light source device 18, taken along the line VII-VII in FIG. 6. Thedischarge tube 24 comprises a cold-cathode tube called a fluorescentlamp. Electrodes 24A made of metal such as Ni or W are arranged in theends of the discharge tube 24. Lean gas (such as Ar or Ne) and mercury28 are inserted and sealed in the discharge tube 24, and a fluorescentmaterial is coated on the inner surface of the discharge tube 24. Thereflector 26 comprises an aluminum mirror, for example, and has across-sectional shape such a U-shape to cover the discharge tube 24.

Support members 25 are arranged on the discharge tube 24 near theelectrodes 24A for supporting the discharge tube 24 to the reflector 26.The inner surface of the support member 25 is in close contact with thedischarge tube 24, and the outer surface of the support member 25 is inclose contact with the reflector 26. A portion of the electrode 24A iswithin the discharge tube 24, and another portion of the electrode 24Aextends to the exterior of the discharge tube 24 through the end of thedischarge tube 24 and the end of the support member 25.

The support member 25 is formed of a heat insulating structure so as toprevent a temperature drop of a portion of the discharge tube 24 nearthe electrode 24A. In this embodiment, the support member 25 is made ofa material having high heat insulating property and high voltagewithstanding property. For example, the support member 25 is made ofAramid fiber. The support member 25 can be made of glass wool.

In the structure in which the discharge tube 24 is supported by thereflector 26 with the support members 25, there is a tendency that heatof the discharge tube 24 is thermally conducted to the reflector 26through the support members 25, and further from the reflector 26 to thehousing of the display device, so that the temperature of a portion ofthe discharge tube 24 near the electrodes 24A may be reduced.

Conventional support members are made of silicone so as to withstand thehigh voltage applied to the electrodes, and the heat of the dischargetube 24 is thermally conducted to the reflector 26 through the supportmembers 25, because silicone has a good heat conductivity, so that thetemperature of the portion of the discharge tube 24 near the electrodes24A may be possibly reduced to the lowest value. Therefore, liquidmercury is collected at the portion of the discharge tube 24 near theelectrodes 24A where the temperature is lowest, resulting in thereduction of the amount of gaseous mercury and a short life of thedischarge tube 24.

In the present invention, the support member 25 is formed of a highlyheat insulating material, so the heat of the discharge tube 24 is not somush thermally-conducted to the reflector 26 through the support members25, and the temperature of the portion of the discharge tube 24 near theelectrodes 24A is not reduced to the lowest value. The portion of thedischarge tube 24 near the electrodes 24A is a portion at which theamount of the generated heat is primarily maximum and the temperature ishigher, and the position at which the temperature becomes lowest in thedischarge tube 24 is shifted toward the center from the region in whichthe support member 25 extends. Therefore, liquid mercury is notcollected at the portion of the discharge tube 24 near the electrodes24A.

On the other hand, metal of the electrodes 24A of the discharge tube 24is sputtered with electrons during discharge and particles of metal ofthe electrodes 24A are deposited on the inner surface of the dischargetube 24. The region in which particles of metal of the electrodes 24Aare deposited on the inner surface of the discharge tube 24 is limitedto the region within a restricted distance from the end of the electrode24A. For example, in the case of the discharge tube 24 having thediameter of 5 mm, the region in which particles of metal of theelectrodes 24A are deposited on the inner surface of the discharge tube24 is within approximately 10 mm from the end of the discharge tube 24or within 5 mm from the end of the electrode 24A.

Liquid mercury is not collected in the region in which particles ofmetal of the electrodes 24A are deposited, so liquid mercury is notcaptured by particles of metal. Therefore, according to the presentinvention, most liquid mercury can continue to evaporate and the amountof gaseous mercury is not reduced, so the operating life of thedischarge tube 24 is not shortened.

FIG. 8 is a sectional view of the light source device 18 including thedischarge tube 24 and the reflector 26 according to a modifiedembodiment, and FIG. 9 is a sectional view of the support member of FIG.8. Support members 25 are arranged on the discharge tube 24 near theelectrodes 24A for supporting the discharge tube 24 to the reflector 26.The support member 25 is formed of a heat insulating structure so as toprevent a temperature drop of a portion of the discharge tube 24 nearthe electrode 24A. In this embodiment, the support member 25 is made ofsilicone, similar to a conventional support member, but the supportmember 25 has a hollow portion 25B to realize a heat insulatingstructure. The operation of this embodiment is similar to that of theprevious embodiment.

FIG. 10 is a sectional view of the light source device 18 including thedischarge tube 24 and the reflector 26 (reflector 26 is omitted in FIG.10) according to a modified embodiment. In this embodiment, thedischarge tube 24 is partially formed of a heat insulating structure soas to prevent a temperature drop of a portion of the discharge tube 24near the electrode 24A of the discharge tube 24. In other words, the endportion of the discharge tube 24 is formed in a double-tube structurehaving an outer tube portion 24 o and an inner tube portion 24 i, sothat a heat insulation part comprising an air layer or a vacuum layer isprovided between the outer tube portion 24 o and the inner tube portion24 i. The support member 25 is arranged around the outer tube portion 24o and supports the discharge tube 24 to the reflector 26. The operationof this embodiment is similar to that of the previous embodiment.

FIG. 11 is a sectional view of the light source device 18 including thedischarge tube 24 and the reflector 26 according to a modifiedembodiment. In this embodiment, the support members 25 are arranged atpositions inward from the ends of electrodes 24A of the discharge tube24 so as to prevent a temperature drop of a portion of the dischargetube 24 near the electrode 24A of the discharge tube 24. As describedabove, the region in which particles of metal of the electrodes 24A aredeposited on the inner surface of the discharge tube 24 is limited tothe region within a restricted distance from the end of the electrode24A. The support members 25 are arranged on the outside of the regionsin which particles of metal of the electrodes 24A are deposited (i.e.,inward positions).

In this case, the support members 25 are not necessarily made of a heatinsulating material, and are made of silicone, for example. Therefore,the temperature is lowest at the portion of the discharge tube 24 wherethe support members 25 are located due to the thermal conduction throughthe support members 25, as described above. However, as the lowesttemperature portion of the discharge tube 24 is out of the region inwhich particles of metal of the electrodes 24A are deposited on theinner surface of the discharge tube 24, so liquid mercury is notcaptured by particles of metal. Therefore, according to the presentinvention, most liquid mercury can continue to evaporate and the amountof gaseous mercury is not reduced, so the operating life of thedischarge tube 24 is not shortened.

FIG. 12 is a sectional view of the light source device 18 including thedischarge tube 24 and the reflector 26 according to a modifiedembodiment. In this embodiment, the light source device 18 comprisessupport members 25 arranged at positions near electrodes 24A of thedischarge tube 24 for supporting the discharge tube 24 to the reflector26, and a heat conduction member 32 contacting a central portion of thedischarge tube 24. The support members 25 are made of silicone. The heatconduction member 32 is made of silicone having higher heat radiatingproperty. Alternatively, it is possible to arrange fins on the heatconduction member 32 or to deliver cooling air from a fan.

The heat conduction member 32 also contacts the reflector 26 andreleases the heat of the central portion of the discharge tube 24 to thereflector 26 to move the lowest temperature portion to the centralportion of the discharge tube 24. Therefore, liquid mercury is notcollected to a portion of the discharge tube 24 near the electrodes 24A,and liquid mercury is not captured by particles of metal. Therefore,according to the present invention, most liquid mercury can continue toevaporate and the amount of gaseous mercury is not reduced, so theoperating life of the discharge tube 24 is not shortened.

Also, by moving the lowest temperature point to the centrer of thedischarge tube 24, mercury 28 evaporates mainly at the lower temperatureportion and resultant gaseous mercury diffuses in the whole dischargetube 24. The diffused gaseous mercury also returns to the lowertemperature portion. In this way, gaseous mercury is uniformlydistributed in the whole discharge tube 24, and the temperature and thepressure of gaseous mercury are substantially uniform in the wholedischarge tube 24. That is, it is possible to control the temperature ofgaseous mercury, by making the lower temperature point. The brightnessof light emitted by the discharge tube 24 becomes maximum at the optimumconcentration of gaseous mercury, and the corresponding temperature, inthe discharge tube 24, and the brightness of the light emitted by thedischarge tube 24 is lower than the maximum value if the concentrationof gaseous mercury is higher or lower than the optimum concentration orif the temperature in the discharge tube 24 is higher or lower than theoptimum value. In this embodiment, it is possible to acquire the maximumbrightness of the light emitted by the discharge tube 24, by moving thelower temperature point in the discharge tube 24 to thereby set thetemperature in the discharge tube 24 at or near the optimum value.

FIG. 13 is a sectional view of the light source device 18 including thedischarge tube 24 and the reflector 26 according to a modifiedembodiment. Support members 25 are arranged at positions near theelectrodes 24A of the discharge tube 24 for supporting the dischargetube 24 to the reflector 26. A layer of heat insulating material (heatinsulating sheet) 34 is arranged between the discharge tube 24 and thereflector 26. The discharge tube 24 is attached to the reflector 26,with the layer of heat insulating material 34 bonded to the supportmember 25. The support member 25 is made of silicone as in theconventional case, and the layer of heat insulating material 34 is madeof meta-type Aramid fiber (Cornex from Teijin Corporation, for example).The support member 25 has a good heat conducting property, but the layerof heat insulating material 34 blocks the heat to thereby prevent theheat from escaping from the ends of the discharge tube 24 to thereflector 26. Therefore, a temperature drop of a portion of thedischarge tube 24 near the electrodes 24A is prevented. The operation ofthis embodiment is identical to that of the previous embodiments.

FIG. 14 is a sectional view of the light source device 18 including thedischarge tube 24 and the reflector 26 according to a modifiedembodiment. Support members 25 are arranged at positions near theelectrodes 24A of the discharge tube 24 for supporting the dischargetube 24 to the reflector 26. A layer of heat insulating material (heatinsulating sheet) 34 is arranged between the discharge tube 24 and thesupport member 25. The support member 25 is made of silicone as in theconventional case, and the layer of heat insulating material 34 is madeof meta-type Aramid fiber (Cornex from Teijin Corporation, for example).The support member 25 has a good heat conducting property, but the layerof heat insulating material 34 blocks the heat to thereby prevent theheat from escaping from the ends of the discharge tube 24 to thereflector 26. Therefore, a temperature drop of a portion of thedischarge tube 24 near the electrodes 24A is prevented. The operation ofthis embodiment is identical to that of the previous embodiments.

FIG. 15 is a sectional view of the light source device 18 including thedischarge tube 24 and the reflector 26 according to a modifiedembodiment. In this embodiment, the reflector 26 is made of a heatinsulating resin, for example, polycarbonate. Polycarbonate is apolyester resin of carbonic and polyhydric alcohol. Polycarbonate usingaromatic alcohol has properties such as a higher melting point (superiorto thermal stability), a higher mechanical strength, and a higherelectric insulation. A reflection layer 26A such as aluminum is coatedon the inner surface of the reflector 26 so that it does not overlapwith the support members 25. Therefore, the support member 25 has a goodheat conducting property, but the reflector 26 blocks the heat tothereby prevent the heat from escaping from the ends of the dischargetube 24 to the reflector 26 through the support members 25. Therefore, atemperature drop of a portion of the discharge tube 24 near theelectrodes 24A is prevented. The operation of this embodiment isidentical to that of the previous embodiments.

INDUSTRIAL APPLICABILITY

As explained above, according to the present invention, it is possibleto provide a light source device having a discharge tube having a longoperating life.

1. A light source device comprising: a discharge tube having at leastone electrode; a reflector; support members in contact with saiddischarge tube, and wherein said support members are positioned so as tomaintain a lower temperature at a portion of said discharge tube betweensaid support members than a temperature of a portion of the dischargetube located near said at least one electrode; at least one supportmember to support said discharge tube to said reflector; and, whereinsaid at least one support member is located inward from an end of saiddischarge tube comprising said at least one electrode so as to prevent atemperature drop of a portion of the discharge tube near said electrode.2. The light source device of claim 1, wherein a heat conduction memberis located in contact with said discharge tube at a portion of thedischarge tube near said at least one electrode so as to prevent saidportion from being the lowest point in temperature.
 3. The light sourcedevice of claim 1, wherein the temperature of said discharge tube islowest at a portion of the discharge tube where said at least onesupport member is located.
 4. The light source device of claim 1,wherein the temperature of said discharge tube is higher near saidelectrode and lower toward the center of said discharge tube.
 5. Thelight source device of claim 1, wherein the support member contacts onlya minority of a length of the discharge tube.
 6. The light source deviceof claim 1, wherein said support member is a ring surrounding a halfcircumference or more of the discharge tube.
 7. The light source deviceof claim 1, wherein said light source device is located in any one ofthe group consisting of: a LCD module, a LCD display, a table topcomputer and a notebook computer.
 8. A display module including a lightsource device, said display unit comprising the light source device asset forth in claim
 1. 9. A display device mounting a light source fordisplaying, said display device comprising the light source device asset forth in claim
 1. 10. An information handling apparatus comprising adisplay module including the light source device as set forth inclaim
 1. 11. A portable information handling apparatus comprising adisplay module including the light source device as set forth in claim1.